The unimolecular decomposition of 3,4dihydro-2H-pyran was investigated behind reflected shock waves by monitoring infrared absorption at 9.44 pm. The decomposition proceeded via a direct molecular process to ethylene and acrolein. The Arrhenius expression for the decomposition rate constant, k= IO"-
The unimolecular dissociation of 3,4-dihydro-2H-pyran over a wide temperature range
β Scribed by G. J. Besseris; J. H. Kiefer; Q. Zhang; J. A. Walker; W. Tsang
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 589 KB
- Volume
- 27
- Category
- Article
- ISSN
- 0538-8066
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β¦ Synopsis
The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C ~H B O ) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10% DHP in krypton over 900-1500 K, 110-560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric, using the decomposition of allylethyl ether as an internal standard, and covering 663-773 K. The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions. Precise rate constants (rms deviation of 10%) were obtained for this process over the indicated temperature ranges. Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff a t the lower temperatures. These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when (AE)down is a fured 400 cm-'. Arrhenius expressions for k, derived from the two measurements are in close accord and also consistent with most previous studies of this reaction.
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